1. Field of the Invention
The present invention relates to electrostatographic fusing apparatus, and more particularly to a fuser roller for use in a heat and pressure roller-type fusing apparatus.
2. Description Relative to the Prior Art
Electrostatographic reproduction machines such as copiers and printers, are well known. Such copiers and printers include pressure and fuser rollers which are used in heat and pressure roller-type fusing apparatus therein for fusing toner images onto a sheet or substrate. For various advantages, and in order to solve various problems, some such pressure and fuser rollers are provided with particular shapes and geometries as disclosed for example in U.S. Pat. No. 3,945,726 issued Mar. 23, 1976 to Ito et al; U.S. Pat. No. 4,042,804 issued Aug. 16, 1977 to Moser; 4,253,392 issued Mar. 3, 1981 to Brandon et al; U.S. Pat. No. 4,594,068 issued Jun. 10, 1986 to Bardutzky et al; and 4,933,724 issued Jun. 12, 1990 to Sugimoto et al.
For example, in the '724 patent the walls of the core of the fuser roller are reduced in thickness for improved heat distribution. In the '068 patent the pressure roller is tapered in order to modify the speed of such a roller relative to the speed of a cylindrical pressure roller. In the '392 patent means are provided for tapering and untapering the ends of a pressure roller in response to changes in ambient humidity. In the '804 patent the pressure roller is tapered in order to achieve faster speeds at its ends in order to prevent copy sheet wrinkling, and in the '726 patent it is suggested to paint the inside of, or otherwise increase the density of the ends of a tubular fuser roller, in order to improve its thermal efficiency at such ends.
Typically, however, each fuser roller that is internally heated includes a generally cylindrical heat conductive metallic core, an internal heat source such as a lamp, and an elastomeric layer made for example of silicone rubber formed over the core. In order to effectively melt and fuse toner images in a fusing apparatus which includes such a fuser roller, the roller must be heated so that its surface reaches a particular temperature control point. The temperature of the surface is usually maintained at such a control point with the help of a temperature sensor which may be positioned on such surface and towards an end of the fuser roller. As is well known in the art, running copy sheets or substrates over sheet contacting portions of the heated fuser roller during fusing periods results in heat dissipation or loss from the surface of the fuser roller to the sheets or substrates.
As such, the temperature of the sheet contacting portions of the fuser roller is likely to be lower than that of the other, for example end portions which are not contacted by the sheets or substrates. Accordingly, during running or fusing periods of the fusing apparatus heat therefore builds up in such end portions of the fuser roller, resulting in high surface temperature surges in the end portions of the fuser roller. The high temperature surges at these end portions of the fuser roller can detrimentally affect the effectiveness of the temperature sensor if located thereat, as described above. In addition, the heat build up causing such high temperature surges can also undesirably cause the metallic core to warp or crack within such end portions. The result, of course, can be less than desired fusing quality due to poor control of fusing nip geometry and pressures, as well as poor surface temperature control, and hardware damage.